1. Field of the Invention
The present invention relates to a non-copiable videotape recording system, and more particularly, to a videotape recording system capable of recording video signal on a tape such, that no copying therefrom to another tape is allowable.
2. Description of the Prior Art
To prevent an illegal copying from one videotape to another, the common practice is to utilize vertical synchro signal kept lower than a normal level when video signals are recorded on a videotape. In trying to copy from this videotape to another by means of a recorder, the synchro signal separator of the recorder cannot be properly operated because of the deliberate weakness of the vertical synchro signal. But it is no problem to reproduce the video signals on a television picture screen by increasing the low vertical synchro signal to a normal level by means of a vertical synchro signal controller incorporated in most of the television receivers.
However, the prior art system has the following disadvantages:
(1) If the synchro signal controller has a sufficient sensitivity to allow the video signals to be reproduced on another tape, the videotape is in danger of being pirated;
(2) It is troublesome to adjust the vertical synchro signal controller each time when the videotape is played back on a television set;
(3) It may happen that the video signals cannot be output because the maximum adjustable level of the vertical synchro signal does not comply with the required level; and
(4) If the television set has no vertical synchro signal controller, it is absolutely impossible to play back the videotape on the television.